Integrated circuits: a chip that controls the rotation of light

Researchers know this well: controlling the light inside a microchip has always been an arduous challenge. The imperfections of the material create reflections and rebounds that affect the direction of rotation of the light, generating noise. In this unfair battle, UniTrento research now marks a turning point with the invention of "Drum", a "Dynamically reconfigurable unified microresonator". Drum is the result of the work of a research group of the Nanoscience Laboratory of the Department of Physics, led by Professor Lorenzo Pavesi, whose results were just published in "Light: science and applications", a journal of the Nature group.

The authors of the article are Bülent Aslan, Riccardo Franchi, Stefano Biasi, Salamat Ali, Davide Olivieri and Lorenzo Pavesi himself. Stefano Biasi and Bülent Aslan, respectively, designed the structure of the microresonator and conducted the experiments. They point out that this work falls within the scope of the «integrated circuits with which light information is manipulated: Drum is an on-chip structure as large as a grain of dust. A ring that closes in on itself, in which light travels clockwise and counterclockwise».

They explain that the device intervenes on the light flow, making it possible to reduce the interference linked to the small impurities of the materials and also to force the movement in the desired direction: «The light is deflected by small irregularities in the silicon. The novelty of our work is that we have introduced two thermally tunable side waveguides on the ring, which enable us to compensate for these effects and use the same structure in different configurations, maintaining precise light control». They add: «In this way, two operating points can be achieved: by keeping the waveguides closed, you can reach the so-called "diabolic point", where you can work perfectly and the signal flows without obstacles, as if it were an ideal ring. When leaving one of the side waveguides open, on the other hand, the structure reaches the "exceptional point": in this configuration, the light is forced to move in a given direction».

In short, Drum works as a sort of tuning knob, a controller that overcomes one of the main challenges of photonics. «A limited control of the working point was already known and consolidated in the field — say Biasi and Aslan —. With this chip, however, we introduce a reconfigurable device that makes it possible to switch in a controlled way from one operating condition to another, making the device extremely flexible».

With their prototype, the researchers open the way to new possibilities. «For example, in the study of more complex non-linear phenomena — they explain —. Thanks to its sensitivity and controllability, the possible applications of the device are in the fields of sensors and controlled memories for neuromorphic computing. In the first case, for the detection of very small particles, for example in biology. In the second field, on the other hand, potential applications are in artificial intelligence. It is known that an optical ring can partly mimic the behaviour of an artificial neuron. Drum offers the possibility of creating an artificial neuron more similar to biological ones».